1. Field of the Invention
The invention relates to a vehicle occupant protection apparatus and, more particularly, to a vehicle occupant protection apparatus, such as a vehicle air-bag system.
2. Description of the Related Art
A generally known air-bag system provides a technology for deploying an air bag at the time when a main G sensor and a safing G sensor both detect a collision of a vehicle in order to prevent erroneous deployment of the air bag. In regard to the above technology, in recent years, an air-bag system that is able to deploy an air bag even when an abnormal condition, such as a fault or a break, occurs in a safing G sensor, which is, for example, suggested in Japanese Patent Application Publication No. 2005-239059 (JP-A-2005-239059).
Hereinafter, an air-bag system that is able to deploy an air bag even when an abnormal condition, such as a fault or a break, occurs in a safing G sensor according to a related art will be described with reference to FIG. 11 and FIG. 12. FIG. 11 is a schematic view of a vehicle equipped with an air-bag system according to the related art. FIG. 12 is a circuit configuration diagram of the air-bag system according to the related art.
As shown in FIG. 11, the air-bag system according to the related art is mounted on a vehicle 1, and includes a pre-crash sensor (PCS sensor) 2, a pre-crash ECU (PCS_ECU) 3, a main G sensor (MG sensor) 4, an air-bag ECU (A/B_ECU) 5 and an air-bag device (AB device) 6.
The PCS sensor 2 is formed of a radar and is mounted at the front of the vehicle 1. The PCS_ECU 3 is mounted inside the vehicle 1. The PCS_ECU 3 estimates the course of a target vehicle on the basis of information acquired by the PCS sensor 2, and calculates the likelihood of a collision of the host vehicle on the basis of the estimated course of the target vehicle. When the likelihood of a collision of the host vehicle increases, and when the collision will occur at the front of the vehicle 1 (frontal collision), the PCS_ECU 3 predicts a frontal collision of the vehicle 1. When the PCS_ECU 3 predicts a frontal collision, the PCS_ECU 3 outputs a signal that indicates the prediction of a frontal collision to the A/B_ECU 5. The MG sensor 4 is mounted at the front of the vehicle 1, and regularly detects a longitudinal acceleration of the vehicle 1. The MG sensor 4 regularly outputs a signal that indicates the magnitude of the detected acceleration to the A/B_ECU 5.
The A/B_ECU 5 is mounted in the middle of the vehicle 1, and activates the A/B device 6 on the basis of the signals output from the PCS_ECU 3 and the MG sensor 4. The A/B device 6 is mounted forward of an occupant A. Specifically, as shown in FIG. 12, the A/B_ECU 5 includes a collision determination unit 51, a safing G sensor (SG sensor) 52, a collision determination unit 53, an abnormal condition determination unit 54, an AND gate 55, an OR gate 56, an AND gate 57, and an air-bag activation unit (A/B activation unit) 58.
The collision determination unit 51 regularly receives the signal output from the MG sensor 4. The collision determination unit 51 regularly monitors the signal output from the MG sensor 4 and, when a rearward acceleration is larger than a predetermined threshold, determines that a frontal collision has occurred. When the collision determination unit 51 determines that a frontal collision has occurred, the collision determination unit 51 outputs a signal that indicates the occurrence of a frontal collision to the AND gate 57.
The SG sensor 52 is mounted inside the A/B_ECU 5, and regularly detects a longitudinal acceleration of the vehicle 1. The SG sensor 52 regularly outputs a signal that indicates the magnitude of the detected acceleration to the collision determination unit 53 and the abnormal condition determination unit 54.
The collision determination unit 53 regularly receives the signal output from the SG sensor 52. The collision determination unit 53 regularly monitors the signal output from the SG sensor 52 and, when a rearward acceleration is larger than a predetermined threshold, determines that a frontal collision has occurred. When the collision determination unit 53 determines that a frontal collision has occurred, the collision determination unit 53 outputs a signal that indicates the occurrence of a frontal collision to the OR gate 56.
The abnormal condition determination unit 54 regularly receives the signal output from the SG sensor 52. The abnormal condition determination unit 54 regularly monitors the signal output from the SG sensor 52, and determines whether an abnormal condition, such as a fault or a break, occurs in the SG sensor 52. When the abnormal condition determination unit 54 determines that an abnormal condition has occurred in the SG sensor 52, the abnormal condition determination unit 54 outputs a signal that indicates the occurrence of an abnormal condition to the AND gate 55.
The AND gate 55 receives the signal output from the PCS_ECU 3 in addition to the signal output from the abnormal condition determination unit 54. When the AND gate 55 receives both the signal output from the abnormal condition determination unit 54 and the signal output from the PCS_ECU 3, the AND gate 55 outputs a signal that indicates the reception of both signals to the OR gate 56. When the OR gate 56 receives at least one of the signal output from the AND gate 55 and the signal output from the collision determination unit 53, the OR gate 56 outputs a signal that indicates the reception of the at least one of the signals to the AND gate 57. When the AND gate 57 receives both the signal output from the collision determination unit 51 and the signal output from the OR gate 56, the AND gate 57 outputs a signal that indicates that the reception of both signals to the A/B activation unit 58.
When the A/B activation unit 58 receives the signal output from the AND gate 57, the A/B activation unit 58 activates the A/B device 6. The A/B device 6 is activated and then deploys the air bag.
In this way, the air-bag system according to the related art, shown in FIG. 11 and FIG. 12, determines beforehand whether an abnormal condition occurs in the SG sensor 52, and, when an abnormal condition has occurred in the SG sensor 52, activates the A/B device 6 at the time when the MG sensor 4 has detected a collision. By so doing, even when an abnormal condition occurs in the SG sensor 52, it is possible to deploy the air bag.
However, in the air-bag system according to the related art, shown in FIG. 11 and FIG. 12, when there is no abnormal condition in the SG sensor 52, the air bag is deployed only when both the MG sensor 4 and the SG sensor 52 detect a collision of the vehicle 1. For this reason, there has been a case in which deployment of the air bag delays against required time within which the air bag must be deployed after a collision.
Hereinafter, the reason why deployment of the air bag delays will be described in detail with reference to FIG. 13. FIG. 13 is a view that schematically shows the operation timings of the MG sensor 4, SG sensor 52 and A/B activation unit 58. In FIG. 13, it is assumed that the PCS_ECU 3 predicts a frontal collision at time t1 and the frontal collision actually occurs at time t2. Because the MG sensor 4 is mounted at the front of the vehicle 1, the MG sensor 4 detects the frontal collision at a timing that is substantially the same as the timing of the actual frontal collision, that is, time t2. On the other hand, the SG sensor 52 is mounted in the middle of the vehicle 1. This delays a timing at which the SG sensor 52 detects the frontal collision from the timing at which the MG sensor 4 detects the frontal collision by a period of time (Δt) during which the frontal collision propagates from the MG sensor 4 to the SG sensor 52. Thus, as shown in FIG. 13, the timing at which the SG sensor 52 detects the frontal collision is time t3 that is delayed by Δt from time t2. The A/B activation unit 58 does not activate the A/B device 6 until the SG sensor 52 detects the frontal collision. Thus, a timing at which the A/B device 6 is activated is the same as the timing at which the SG sensor 52 detects the frontal collision, that is, time t3.
In this way, the timing at which the A/B device 6 is activated delays by propagation time Δt. In accordance with this, deployment of the air bag also delays by the propagation time Δt. This has sometimes caused a delay of deployment of the air bag against the time required for deployment. Particularly, when the MG sensor 4 is mounted at the side of the vehicle 1 and then a side air bag is deployed at the time of a side collision, time required for deployment of the air bag is shorter because the distance from a collision location to the occupant A is short. For this reason, when the side air bag is deployed at the time of a side collision, there have been many cases in which deployment of the air bag delays.